Simulated wood transfer films are used for providing the appearance of real wood grain to many surfaces including furniture, countertops, walls, siding and automobiles. In order to enhance the wood-like appearance of such films, those skilled in the art have employed various methods to simulate the texture and grain pattern of real wood. The roughened texture of natural wood is a result in part of small indentations or slash marks present throughout the grain pattern known as tick marks.
Early methods for simulating a natural wood design involved embossing to form a series of depressions in the wood grain pattern provided on film as described, for example, in U.S. Pat. No. 3,452,861 by Ervin.
U.S. Pat. Nos. 3,666,516, 3,770,479 and 3,953,635 by Dunning utilized indentations in combination with a change in specular reflectance, i.e., gloss level, on heat-stamped simulated wood film to improve upon merely embossed depressions. While improving upon methods of providing ticks by mere indentation, adding a change in gloss level still does not provide a sufficiently realistic simulation of a real wood tick pattern, because the optical effect is not sufficiently perceived when viewed from an angle perpendicular to the plane of the film. The maximum optical effect from such a tick is perceived when viewed at an angle of approximately 45.degree. to the plane of the film.
The reason a natural tick can be perceived at varied angles is that in addition to the actual depression or indentation in the wood surface, a color is present in the indentation. Thus, the appearance of the optical effect of an indentation would be enhanced if the areas of lower gloss level also possessed coloration.
A simulated wood film is manufactured by providing individual coatings or layers to a polymer film. Wood patterns are created by providing various consecutive ink prints in alignment with one another upon the film by gravure roller. The pattern is kept in alignment, or registration, by varying methods of process control. Manufacturers have attempted to register a coating providing the optical tick marks and a second further coating which provides coloration to those marks. These attempts have not been successful due to the small size of the marks and the degree of registration currently attainable by available methods of process control.
One such early attempt is found in U.S. Pat. No. 3,936,570. In the transfer material described in that patent, gaps are made in a fully releasable stripping layer adhered to a carrier sheet. A design coat which may cover the entire stripping layer or only the gaps is then coated on the stripping layer. When the carrier sheet is removed, the stripping layer fully remains on the transferred wood film and a portion of the design layer is torn away with the carrier creating an uneven physical embossing on the surface of the transferred film. While the design layer may optionally contain pigment and provides a change in specular reflectance, it is unevenly depressed beneath the surface of the film and the stripping layer incompletely covers the surface of the film.
There is a need in the art for a simulated wood transfer film having a tick pattern which more closely resembles that of the indentations in real wood due to the presence of color and a lower gloss within the tick marks, but which does not require embossing or gaps in the protective covering.